Polyoxyethylene-base nonionic compounds have been known for long to be useful as surfactant and detergent, and their physical properties and emulsifying, solubilizing and cleansing characteristics have been studied and reported in fair detail (see Martin J. Schick, NONIONIC SURFACTANTS, PHYSICAL CHEMISTRY (1987) and so on).
Such polyoxyethylene-base nonionic surfactants have high detergency and can also be used favorably in a state combined with other ionic surfactant, so that various combinations thereof with other surfactants have been proposed.
However, the polyoxyethylene-base nonionic surfactants according to the prior art have the property of bringing about high foaming and slow defoaming, and this property is unsuitable for use in automatic dish washers, the demand for which has recently increased, use as industrial detergents and use in drum washing machines. Under such circumstances, it has been expected to develop a nonionic surfactant which has high detergency suitable for the above uses and exhibits both low foaming properties and rapid defoaming properties. In order to satisfy these requirements, there have been reported nonionic surfactants wherein low foaming properties are attained by combining ethylene oxide with other alkylene oxides. For example, ethylene oxide/propylene oxide block adducts are proposed in JP-B 60-12000, and block adducts having narrow ranges of distribution of polymerization are proposed in JP-A 6-303825. Further, surfactants wherein the terminal hydroxyl group is blocked with an alkyl group are proposed in JP-A 47-788. However, blocking the terminal of such a surfactant with propylene oxide or a short-chain alkyl group causes the problem of lowering the detergency of the surfactant remarkably, though it is effective in depressing the foaming properties.
With respect to household and industrial detergents, meanwhile, a formulation having a higher surfactant concentration has been required from the standpoints of energy saving in the production or transportation, resource nursing, and diminution in the containers to be disposed of.
When the content of a nonionic surfactant in a detergent lies in a higher range, however, the viscosity of the detergent is sharply increased or decreased even by a little difference in the surfactant content. Therefore, there occur such problems that an extremely high-accuracy metering is required in order to keep the properties of the detergent constant and that it is difficult to keep the detergent at a constant viscosity in storage. Under these circumstances, it has been expected to develop a surfactant composition which contains a nonionic surfactant and which exhibits low foaming properties and rapid defoaming properties and has high detergency and a low and stable viscosity.
U.S. Pat. No. 4134854 discloses a specific polyalkylene oxide adduct as a low-melting nonionic surfactant. However, this US Patent Specification is silent on the favorable concentration of the surfactant composition containing this adduct. U.S. Pat. No. 3,567,784 discloses that another specific polyalkylene oxide adduct is a nonionic surfactant having a high cloud point and a low gelation temperature. However, this US Patent Specification is silent on the high-concentration surfactant composition containing this adduct, so that the viscosity behavior of the composition cannot be inferred. Furthermore, JP-A 47-9561 (corresponding to U.S. Pat. No. 4115457) discloses a process for the preparation of another specific polyalkylene oxide adduct which is useful as a scouring agent or dyeing aid. J.A.O.C.S,vol.63,No.9,pp 1201-1208(1986) discloses similar polyalkylene oxide adducts as above.